By Danielle Kurtzleben

The nation's grid is ready. Your neighborhood's power supply might be another story

Buried beneath the defense reductions and tax increases in the president's new $3.8 trillion budget is another initiative getting less attention: increased incentives for electric car purchases. President Obama is proposing that the tax credit for an electric car purchase be raised from $7,500 to $10,000. That, along with fears of sky-high gas prices, could drive purchases up...but some city power grids may not be able to handle a new fleet of plug-in cars.

Depending on how you parse the figures, an electric vehicle's power usage can sound either negligible or massive. The all-electric Nissan Leaf, for example, has a 3.3 kW charger, roughly equal to the usage of a clothes dryer or two hair dryers. But added up, the amount of energy that car uses can be far greater. Running a clothes dryer all night, half the time it takes to fully charge a Leaf battery on a standard home outlet, could make for a substantial increase in a household's electric bill.

According to the EPA, a Leaf consumes around 340 watt hours per mile. Charge that car enough to drive 30 miles per day, and that's more than 306 kilowatt hours per month, nearly one third of the national average home energy usage of 958 kilowatt hours, according to the Department of Energy. The addition of three new Leafs with this driving pattern, then, would be the equivalent of adding another household onto an electrical grid.

Depending on the home, driver, and electric vehicle in question, the amount of energy consumed can be even greater. "One vehicle's demand can be anywhere up from three quarters of a house up to three houses," says Jay Tankersley of Project Get Ready, a non-profit working to help cities prepare for increased electric vehicle usage.

Many experts agree that, on a national level, the United States is ready for a vast expansion in electric cars. According to a 2008 Energy Department study, the effect of a vast expansion in electric vehicles could be minimal. Electric vehicles are expected to account for around one quarter of the market by 2030. If those vehicles are all charged after 10 p.m., when electricity demand is low, the nation would require no additional power generation. Then again, if all owners charged their cars at 5 p.m., up to 160 new large power plants would be necessary.

The nation as a whole might have the capacity, but on a neighborhood-by-neighborhood basis, the problem is more pronounced. "In most residential areas, an EV can easily be accepted into the charging infrastructure. [But] as soon as you start getting clustering of vehicles, they can't have too many of those in one area without some kind of a strategy for adapting to it," says Alan Schurr, vice president of strategy and development for energy and utilities at IBM.

As people of similar incomes, not to mention mindsets, can often group together in neighborhoods, electric vehicles can also tend to be purchased in geographic clusters. That effect, which some have called the "Prius cluster," is already a consideration for utility companies in California, as Business Insiderreported last year.

Consider what happens in a typical city neighborhood on a hot August evening: one too many air conditioning units overloads the transformer and knocks out power. A few electric vehicle clusters could have the same effect. A substantial increase in electric vehicle sales, then, would produce fewer emissions, but also a few city blocks of angry neighbors.

So while electric vehicle buyers can see significant savings on gasoline -- a gas-powered vehicle can be three to five times as expensive as an electric car, according to the Energy Department -- they could also, depending on their city's infrastructure, also suffer some inconveniences.

More than 2,400 public and private charging stations have popped up nationwide, according to the Energy Department, but home charging is still the top choice for EV owners. Around 80 percent of plug-in electric vehicle users charge at home, says Tankersley, meaning that residential areas bear the brunt of vehicles' electricity usage.

Car companies have made strides toward lessening the burden on electric grids. "The evidence so far for the early users of EVs is that they're very willing to offset the timing of that recharge until after the afternoon peak has passed," says Mark Perry, director of product planning for Nissan. Therefore, some electric cars feature programmable charging, allowing owners to plug in their car in the evening, but with battery charge starting at an off-peak time like 11 p.m.

Bringing home a new electric vehicle may not make the neighborhood go dark just yet, in other words, but that could change in coming decades.

"At the scale that we're at now it's not an issue but it will be if it's not managed in some way," says Schurr. According to a 2011 Department of Energy report, the estimated production of electric vehicles in the U.S. in that year was just over 45,000 -- a slim figure compared to the 12 million light-duty vehicles sold in 2010. However, the load of EVs on the road by 2015, said the report, could be at 1.2 million.



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Driving Today: City Grids May Not Be Ready for Electric Cars